If you’re reading, clicking, and breathing right now, odds are you’re the proud owner of billions of neurons. Why not show some neuronal pride by learning a little about the cells that make your world go round?
Neurons are specialized cells in the brain and throughout the body. Because they are electrically excitable, neurons can relay signals through electrical impulses. Like all cells, neurons have a cell body or soma that contains the nucleus, which holds the bulk of the cells genetic material (here’s an actually helpful link). One end of a neuron’s soma has branch-like dendrites, used to receive signals from other neurons. The other end tapers into a long, pipe-like axon, which allows the neuron to relay electrical signals longer distances. The axon ends in the axon terminal, where more branch-like arms form synapses or connections with the dendrites of neighboring neurons or other kinds of cells.
Neurons actually relay information through a process called action potential. When a stimulus reaches a neuron’s dendrites, it causes a change in the cell’s internal concentrations of potassium (K+) and sodium (Na+) ions. If this change is great enough, an action potential begins.
Normally, and axons membrane has a negative charge on the inside and a positive charge on the outside. Initially, there’s a lot more sodium outside the cell than in. When an action potential begins, it pops open voltage-gated sodium channels – basically, tiny pores that only allow sodium ions through. Because there’s much more sodium outside of the cell, sodium floods in through the channels because of diffusion.
These channels close quickly, but the increase of positive sodium ions makes the inside of the cell positive and the outside, negative. This change in charge causes voltage-gated potassium channels to open next. Potassium ions are positive; the inside of the cell is suddenly also very positive; positive charges repulse each other. This repulsive force causes potassium to rush out of the cell through the channels, restoring the initial configuration of negative inside, positive outside. Likewise, ion pumps exchange sodium inside the cell for the potassium the flooded out.
Meanwhile, leftover sodium flows down the axon, changing the charge inside the cell as it goes and causing more voltage-gated sodium channels to open further down the axon. This process continues until the signal reaches the axon terminal, causing the neuron to release vesicles – little membrane bubbles – of neurotransmitters – chemicals that either excite or inhibit neighboring neurons, sometimes causing the chain of action potential to continue. After a refractory period, the cell is ready for another action potential.
This complicated process is happening thousands of times per second in each of our bodies. Although this is a little mind-blowing, try to not to spend all your time thinking about how much goes into you being able to think. With so much machinery at work, you never know what that much thinking about thinking will do to you.
